Benzo[a]pyrene (BaP) is an environmental pollutant. Besides inducing cancers in humans, BaP has been shown to promote the development of atherosclerosis, which is the primary cause of coronary heart disease and stroke. The mechanism underlying the atherogenic action of BaP remains unknown. A currently popular theory postulates atherosclerosis as an inflammatory process driven by reactive oxygen species (ROS), such as superoxide and hydrogen peroxide. BaP has been shown to increase intracellular ROS. Thus, the project described herein hypothesizes that generation of ROS in vascular cells is a key mechanism by which BaP promotes atherogenesis. Our laboratory has generated mouse models that overexpress Cu/Zn-superoxide dismutase (Cu/Zn-SOD) or catalase alone, or both Cu/Zn-SOD and catalase. Cu/Zn-SOD is a protein that converts superoxide to hydrogen peroxide, while catalase destroys hydrogen peroxide by converting it to water. As the relative contribution of different ROS to atherosclerosis might vary, our animal models provided a valuable tool for testing the role of superoxide and hydrogen peroxide in BaP-induced atherosclerosis. The transgenic mice overexpressing Cu/Zn-SOD and/or catalase have been crossbred into the apolipoprotein E (ApoE)-deficient mice, which spontaneously develop atherosclerotic lesions with morphological features closely resembling the atherosclerotic lesions that occur in humans. In this project, the ApoE-deficient mice, with or without overexpression of Cu/Zn-SOD and/or catalase, will be treated with BaP. We will determine: (1) whether overexpression of antioxidant enzymes inhibits BaP-induced atherogenesis and reduces the accumulation of inflammatory cells within the atherosclerotic lesions, (2) whether overexpression of antioxidant enzymes reduces BaP-induced accumulation of oxidized lipids and nitrotyrosine in the arterial wall, and (3) whether overexpression of antioxidant enzymes reduces BaP- induced atherogenic events in vascular cells, and inhibits BaP-induced gene expression and transcriptional factor activation. If our hypothesis described above is correct, BaP-induced atherosclerotic lesions will be smaller in mice overexpressing Cu/Zn-SOD and/or catalase, which will correlate to a decreased oxidative injury in the arterial wall and/or a reduced response of vascular cells to BaP.